Palm-sized gearbox goes boldly into space

01 April, 2002

Palm-sized gearbox goes boldly into space

A tiny, custom-designed gearbox has played a critical role in ensuring the success of the European Space Agency`s largest ever satellite, which was launched from French Guiana earlier this year. The £1.2bn Envisat environmental monitoring satellite is designed to make the most complete set of earth observations ever performed by a satellite.

A critical element on board the satellite is its 70m2 solar power array which generates up to 8kW to keep its vital instruments working. The array was unfolded once the satellite was in orbit using a battery-powered motor and a cable pulley system. The motor`s output was routed through a gearbox developed for this role by David Brown Engineering (DBE).

The 10cm-diameter gearbox contains an epicyclic gear train of a two-stage sun and triple-planet wheel arrangement, giving an overall ratio of 38:1. The gearbox had to produce a maximum power-to-weight ratio from as small a package as possible, to minimise the impact on the satellite`s payload.

Reliability was also crucial. "The small gearbox only had to operate once, but it had to work with absolute certainty in a harsh environment, and following the stresses imposed by a rocket launch," says Phil Dalton, DBE`s technical sales manager.

DBE inherited the Envisat project when it bought Alvis Transmissions in 1998. Alvis had already begun work on the design and development continued during and after the takeover. David Brown is now supplying similar gearboxes for another ESA project - the Metop series of weather and climate monitoring satellites, the first of which is due to be launched in 2005.